This invention relates to a method of producing a frothed liquid. Particularly but not exclusively it relates to a method of producing a self-foaming beverage for immediate consumption by a consumer, such as a self-foaming refrigerated milk shake drink. It also relates to a method of frothing more viscous liquids to produce a whipped effect, for example to produce whipped cream.
It is well known that mixing of liquid beverages with various gases produces popular types of drink, such as carbonated water, xe2x80x9cfizzyxe2x80x9d lemonade and even self-foaming beers and lagers. Conventionally, in production plants, these types of beverages are produced by filling into individual containers such as bottles or cans from a refrigerated saturation tower. In these well known saturation towers the liquid flows down through numerous platelets or glass balls in the tower, which increase the surface area of the liquid, while gas surrounds and is absorbed into the liquid.
When the beverage reaches the bottom of the saturation tower it is dispensed by bottom filling into the container leaving only a minimal xe2x80x9cheadspacexe2x80x9d above the beverage. xe2x80x9cHeadspacexe2x80x9d is defined to be the liquid-free space inside the container above the surface of liquid in the container.
This method is in common use for the above-mentioned drinks, and its use has been suggested for milk and milk-based products, for example by the method disclosed in Patent document WO 96/33618.
However introducing gas into milk or similar liquids by such a method has the significant disadvantage that, prior to capping of the product, when it is opened to the atmosphere during the filling process the gas expands and is released at such a rate as to cause overflow of the beverage out of the container, due to the absorption time required for a milk-type product to be saturated with gas in a saturation tower being undesirably long. For example, the absorption time may be up to an hour at 9xc2x0 C. for nitrous oxide into milk, compared to 2xc2xd minutes for carbon dioxide into water. Furthermore if the product fill is reduced to say one third of the container capacity with two thirds headspace to allow expansion of the product for drinking from the container, for example using a straw, then the problem arises that the saturated gas leaves the product on storage to fill the headspace leaving the beverage itself with insufficient gas to create a self-foaming effect.
It would be desirable to have a method of producing a self-foaming beverage without pre-dissolving the gas in the liquid and which provided the consumer with a palatable drink on breaching the beverage container.
According to a first aspect of the present invention there is provided a method of producing a frothed liquid comprising the steps of filling a container with the liquid leaving a headspace above the liquid, introducing pressurised gas into the headspace and sealing the container.
The container is preferably then left for a period of time during which the gas is absorbed into the liquid. The period of time may be 24 hours during which the contents of the container reach equilibrium at ambient temperature, for example while the product is transported to a retail outlet. Alternatively, or in addition, the container may be shaken during or after filling to increase the absorption rate of the gas into the liquid. The liquid may also be cooled to reduce absorption time. Once the container is shaken and the seal is breached the beverage may foam up to substantially fill the container and be ready to be consumed, for example through a drinking straw or by pouring the beverage directly into a glass. Alternatively the frothed liquid may be released via a valve mechanism provided on the container.
Preferably the liquid used in the method is one having a high viscosity, for example a viscosity higher than that of water such as the viscosity of cream at ambient temperature. This helps trap expanding gas bubbles after the container is breached, thereby prolonging the stability of the foamed beverage. The liquid may, for example, have a high fat content. Most preferred examples of liquids are milk, yoghurts, creams and any of the foregoing containing alcohol, such as milk-based liqueurs. Examples would be GODET (RTM) or BAILEYS (RTM) liqueur.
Preferably the container is a plastic bottle. The plastic may be polyethylene terephthalate (PET). This has the advantage of being much cheaper than an aerosol can, for example. The plastic bottle may be fitted with a conventional lid modified by the inclusion of a valve. The valve may be a standard aerosol valve. It may be a tilt valve. In another example, the container may be of glass.
In the example where the liquid is cream, the method of the present invention produces cream having a whipped texture and appearance.
Preferably the container is for a single use only. For example, when a customer purchases the container with cream or liquid therein, they use it only once to produce whipped cream or frothed liquid, and do not store the container, part full, for any future use.
This overcomes the problem of the cream (or other liquid) becoming frothed inside the bottle, as can happen when a relatively small amount of cream (or liquid) is left in the container between uses. Alternatively, the container may be provided with design features for urging any liquid (which may be frothed) toward the container opening to allow for further use of the container.
In another example, the container may be a tub. The tub may have liqueur and/or cream therein, so that when breached, a blancmange-type dessert is produced.
Preferably the container and its contents are stored at a temperature below room temperature.
Preferably the gas is nitrous oxide.
Preferably the headspace is between 10% and 90% of the total volume of the container. For example the headspace may be between 50% and 80%.
Preferably the gas is pressurised between 20 psi and 150 psi. For example, the gas in the headspace may initially be at a pressure of 120 psi (for cream in a PET bottle with a tilt valve fitted).
In a preferred embodiment the headspace is approximately 67%, being two thirds of the volume of the container. In the preferred embodiment the liquid takes up about one third of the container. Typically the gas is introduced under pressure of approximately 60 psi (4 bar).
Preferably the container is purged with the gas prior to filling with the liquid. The gas is typically pressure filled into the headspace. Alternatively it may be volume filled.
Preferably, the gas is filled into the headspace in the container via a one-way valve in the container. For example, where the container is a bottle, the one-way valve may be provided in the lid of the bottle. The one-way valve may be a rubber plug in the container. In the case of a rubber plug, the gas may be filled by insertion of a needle through the plug. On removal of the needle, the container is sealed. Alternatively the valve may be a single hole to the exterior of the container and one or more holes to the interior which are offset from the exterior hole. The interior holes may be on a platform spaced from the exterior hole, for example by a rubber stopper. In this case, the gas is filled through the exterior hole and reaches the inside of the container via the interior holes. The pressure of the gas inside the container then pushes the platform into contact with the container, forming a seal. As a further alternative, a standard rubber mushroom valve may be used.
Preferably the container is provided with a device for injecting a beverage-enhancing liquid into the container upon breach of the seal. The beverage-enhancing liquid may be coloured or flavoured. Typically when the seal is breached, the beverage-enhancing liquid is fired out of said device, hits the surface of the main liquid from and then mixes into the liquid during the foaming process. For example, a modified version of the device disclosed in Patent document WO 97/21605 may be used.
Preferably the container is provided with a drinking straw device which rises up in the container when the seal is breached forcing the straw into a position for drinking.
According to a second aspect of the present invention there is provided a beverage package comprising a container means having a closable top opening, cap means for capping the top opening of the container means to close and seal the container means in a substantially leak-proof manner, the cap means being selectively detachable from the top opening of the container means to unseal and open the container means, a quantity of foamable beverage initially within the container means, foaming means for foaming at least part of the quantity of beverage upon uncapping and opening of the container means, a drinking straw means disposed initially entirely within the container means, and interaction means attached to or forming part of the drinking straw means for interacting with the foaming beverage upon uncapping and opening of the container means to raise part of the drinking straw means through the now-open top of the container means.
The interaction means may comprise baffle means extending radially outwards from the drinking straw means to interact with the flow of rising foaming beverage upon the opening of the container means whereby to apply a lifting force to the drinking straw means. The baffle means may comprise turbulence-promoting means for promoting turbulence in the beverage and/or in the foam upon opening of the container. The interaction means preferably has the form of an impeller fan disc clipped around the drinking straw means part-way up the height thereof. The interaction means (of whatever form) is preferably formed and dimensioned, and preferably has a location in the drinking straw means, such as to prevent or impede the drinking straw means rising completely through the open top of the container means.
According to a third aspect of the present invention there is provided a beverage package comprising a container means having a closable top opening, cap means for capping the top opening of the container means to close and seal the container means in a substantially leak-proof manner, the cap means being selectively detachable from the top opening of the container means to unseal and open the container means, a quantity of foamable beverage initially within the container means, foaming means for foaming at least part of the quantity of beverage upon uncapping and opening of the container means, a drinking straw means disposed initially entirely within the container means, and turbulence inducing means disposed within the container means for inducing turbulence in the foaming beverage upon uncapping and opening of the container means.
The turbulence inducing means is preferably tethered within the container means or attached to a fixed point within the container means. The turbulence inducing means may take the form of baffle means to interact with the flow of rising foaming beverage upon the opening of the container means in a manner to induce turbulence in the foaming beverage, and preferably in a manner which enhances mixing of beverage components.
The foaming means in the second and third aspects of the invention may comprise a quantity of gas dissolved in the beverage in a concentration sufficient that depressurisation of the interior of the container means upon uncapping thereof induces gas to come out of solution to generate foam. Alternatively, or additionally, the foaming means may comprise an auxiliary container means initially containing pressurised gas releasable from the auxiliary container means into the beverage upon uncapping of the container means. The gas comprised in the foaming means may be an individual gas or a mixture of gases selected from the group of gases including (but not restricted to) carbon dioxide, nitrogen, and nitrous oxide.
In the second and third aspects of the invention, the beverage comprised in the beverage package may be an comestible liquid or mixture of liquids, but is preferably a milk-based beverage. Such a milk-based beverage may be whole milk or semi-skimmed milk or skimmed milk, with or without minor additives such as flavourings, sweeteners, and colourings; however, it is preferred that the milk-based beverage contains a substantial proportion of ethanol (ethyl alcohol), for example in the form of an alcoholic wine or an alcoholic liqueur. The milk-based beverage is preferably a naturally thick beverage, for example a yoghurt, but thickeners may optionally be added to achieve a requisite viscosity in the beverage.
According to a fourth aspect of the present invention there is provided a beverage package comprising a container means having a closable top opening, cap means for capping the top opening of the container means to close and seal the container means in a substantially leak-proof manner, the cap means being selectively detachable from the top opening of the container means to unseal and open the container means, a quantity of foamable beverage initially within the container means, foaming means for foaming at least part of the quantity of beverage upon uncapping and opening of the container means.